The sun is the most important object to Earth.
Without the sun, life could not exist. There would be no heat, and all of the
oceans would be frozen. There would be no light, and all plants would die. There
is almost nothing more important to Earth than the sun.

The sun is an averaged-sized type
G star and is middle-aged at about five billion years. Yet within our home
solar system, the sun contains more than 99% of all matter. As for its size,
about 915 Jupiters could fit in side of it, as could
about 1,206,885 Earths.

Birth

About 5.5 billion years ago, a passing star or galaxy disturbed
a calm and placid cloud of gas and dust, called a nebula.
The star or galaxy caused the cloud to swirl around, causing small eddies to
form.

The swirl caused the gas to start to coalesce together in places.
Gravity, one of the universe's four fundamental forces, caused more and more
gas and dust to gather onto these masses. The masses kept getting bigger and
bigger. At this stage, they were called protostars.
As gravity caused the material to pile on, it also caused those lumps to condense,
which increased their gravity. The condensation caused the pressure in their
cores to rise, and their internal heat increased.

When the heat reached a temperature of 10,000,000 K (18,000,000° F),
nuclear fusion started, and our sun was born.

Energy

The sun creates its energy the same way all other stars do,
through a process known as nuclear fusion, which joins two atoms of hydrogen
to create a helium atom, the excess energy being radiated off into space.

In
the picture to the right, two protons join
together to form a deuterium nucleus, which is also known as "heavy water." A positron and
a neutrino are released
as by-products. The deuterium nucleus is bombarded by another proton, creating
a helium-3 nucleus. The by-product of this is a photon in
the form of a gamma ray (a
very high-energy form of light). Then, the helium-3 nucleus in bombarded by another
helium-3 nucleus, creating a normal helium-4 nucleus. The by-product of this
are two protons, which are free to start the whole process over again. The positron
will be destroyed and form another gamma ray; the energy from this in the form
of gamma rays is radiated out of sun's core.

Every second, the sun converts 500 million metric tons of hydrogen
to helium. Due to the process of fusion, 5 million metric tons of excess material
is converted into energy in each second. This means that every year, 157,680,000,000,000
metric tons are converted into energy. The material from one second of energy
is about 1x1027 (one octillion thousand) watts of energy. On Earth,
we receive about 2/1,000,000,000 (two billionths) of that energy, or about 2x1018 (two
quintillion) watts. This is enough energy to power 100 average light bulbs for
about 5 million years -- longer than humans have been standing upright.

The Light We See

The light that is currently reaching the Earth was generated
in the sun about 100,000 years ago. It takes that long to get to the surface
of the sun because the sun is so dense, and so the escaping energy has a much
harder time escaping. This is analogous to walking down a hallway that was crowded
with people. You couldn't just run right on through, for you would be shoved
back by people and be bounced around. A photon of light encounters this same
resistance when it tries to escape from the sun's core. The other people are
the atoms that make up the sun and other photons generated by nuclear fusion,
the process of which is stated above.

When the light formed in the sun finally makes it to the surface,
it zooms away at 300,000,000 meters per second (186,000 miles per second), making
it to Earth in about 8 minutes and 26 seconds.

The light from the sun is made up of many colors, called the visible
spectrum, and many shorter and longer wavelengths of light. These other
wavelengths are invisible to humans, but they can be measured with special
detectors. The diagram below represents the electromagnetic spectrum, with
the scale being in Hz - oscillations per second.

These other wavelengths consist of Infrared (IR), Ultraviolet
(UV), Micro, Radio, X, and Gamma. (IR light rays can be produced by specially-modified
light bulbs, and are used in many places that sell food.) IR rays heat up matter.
Our atmosphere acts as an "infrared shield," and keeps this light from
reaching the surface. UV light has become an increasing concern over the past
few years. It is a form of radiation, and the hole in the ozone layer is allowing
some of the normally blocked UV light to get through. UV light causes tans, sunburns,
and skin cancer. Micro waves are put to use in most people's kitchens in the
aptly named "microwave." They are used to heat foods quickly, and are
more effective at doing so than IR. Radio waves are used in a whole branch of
astronomy, for they can penetrate clouds of gas and dust that visible light can't.
They are also used for transmitting radio and television shows - television having
a slightly higher frequency. X-rays are a form of radiation that are more powerful
than UV, and are normally blocked by our atmosphere. X-rays are mainly used for
medical purposes. Since they are a form of higher energy, they can penetrate
denser objects than visible light can. Gamma rays are the most energetic form
of radiation, and can pass through the human body. In cells, they can cause mutations
and other severe damage. Luckily, they are blocked by our atmosphere. If they
weren't, human life would be impossible.

Anatomy

The
sun is made up of several layers, which do not have distinct borders separating
them. However, each layer has unique properties, which are vital to the sun's
functions.

In the picture to the left, the black circles show a separation
between the layers.

The center of the sun, the Core, is the only part of the sun
that actually makes energy. The temperature in the Core is about 16,000,000 K
(28,800,000 °F).

The next layer of the sun is the Radiative Zone, which is where
most of the harmful gamma rays bounce around until they become less energetic
forms of light. The temperature here is about 5,000,000 K (9,000,000 °F).

The layer that is next is called the Convection Zone, where
solar material rises and falls due to heating and cooling. The temperature here
reaches only 5,800 K (10,000 °F).

The next section of the sun is called the Photosphere, which
is actually what you see when you look at the sun. Earth's crust is like the
sun's photosphere. The Photosphere is about 400 km (250 miles) deep.Sunspots
occur on the photosphere. This is the place on the sun where the energy created
can finally escape into space. This portion of the sun reaches temperatures of
11,000 K (20,000 °F).

The next layer is the lower part of the sun's atmosphere, the
Chromosphere. It is only visible during a total solar eclipse, when the moon
blocks the light from the Photosphere. It stays about the same temperature as
the Photosphere, 11,000 K (20,000 °F), but is very thick at about 2500 km
(1600 miles).

The last layer of the sun is called the Corona, and it is the
upper layer of the sun's atmosphere. Like the Chromosphere, it is only visible
during a total solar eclipse, such as in the picture at the right. This portion
of the sun is about 1,700,000 K (3,000,000 °F).

Phenomena

Sunspots
are cooler areas of the sun's Photosphere. They also have very strong magnetic
fields, up to 10,000 times that of Earth's, and up to 3000 times the rest of
the sun. Sunspots usually occur in pairs, and can be as large as the planet Earth.
They are about 5,000 K (8,500 °F), which is 6,400 K (11,500 °F) cooler
than the rest of the Photosphere. They have been known since ancient times. They
were not found to be caused by strange magnetic fields until 1908, by George
Ellery Hale.

Sunspots have an eleven-year activity cycle. They peaked last
in 2001, and had their last big dip in 1995. If you own a telescope and a solar
filter, you should see a decreasing amount of sunspots right now, with the next
peak in 2012. No one yet knows why the sun has this "internal clock."

When sunspots are at their peak, the sun actually becomes brighter.
This is because magnetically brighter areas surround each sunspot, more than
making up for the dimmer areas.

Along with the eleven-year sunspot cycle, there appear to be
huge lows where sunspot activity is extremely minimal, lasting about a century
every 200-300 years. The last one was between 1640 and 1715. There are highs,
too, with the last one occurring in the twelfth century.

One way that astronomers know this is from past observation.
Also, astronomers can tell how much the magnetism dropped or rose by studying
the radioactive carbon-14 preserved in the 8,000-year-old trees.

Solar flares are huge outbursts of solar material, which are
several miles long. If we had some way of capturing all the energy emitted in
one of the smallest solar flares, we would have enough energy to power the Earth
for one million years.

A
prominence is a huge loop of solar material extending from the sun. Again, these
are several miles wide and tall.

Death

The sun, a type G star, will die in
about five billion years. The sun will have used up most of its hydrogen, and
its core will have become denser than it now is. Because of this pressure, the
sun's core will heat up to 100,000,000 K (180,000,000 °F), instead of its
normal 10,000,000 K (18,000,000 °F). This will cause the sun to expand so
much that it will envelop Mercury and Venus,
and also vaporize Earth. The sun will be known as a red giant. Its color will
have changed from yellow to orange-red.

The swelling is due to the heat: When any matter gets heated,
it expands. The sun's intense heat will be enough to fuse the helium into larger
atoms, and as long as its helium supply lasts, it will continue to shine - about
100,000,000 years.

During this time, however, the sun will begin to shrink, due
to its lessening mass. When its fuel runs out, it will become a white
dwarf - a star that shines because it is hot, not because it is producing
energy through fusion.

When the sun runs out of heat, it will be a huge, black, chunk
of carbon, floating in space. It will be called a black
dwarf - a dead star.